The great fish migration has begun

Rising sea temperatures are pushing shoals of fish hundreds of kilometers from their native grounds, with warm-water fish now landing in northern nets

By Robin McKie / The Guardian

“Unless we find ways to adapt quota agreements speedily and efficiently, we are going to see a lot more disputes like this one in [the] future,” Roberts said.

This point is highlighted in the study led by Pinnegar, which revealed that anchovy stocks are now spreading along the south coast of England. Talks are taking place to determine whether French or Spanish boats can fish for these — on the grounds that these stocks are extensions of existing populations from the south. Others argue that the new anchovy stocks are a separate population that is only now rebounding in numbers thanks to greatly improved climatic conditions, and that French and Spanish boats should be allowed only restricted access to them.

The “anchovy wars” are looming, it would seem.

In addition to overfishing and warming sea temperatures, marine creatures face a further danger — ocean acidification. Increased amounts of carbon dioxide, pumped into the atmosphere from cars and factories, are being absorbed by the oceans, making their waters more acidic. The impact on coral reefs, which provide homes to thousands of different species of fish, is already being felt. Last year, it was reported that a rare underwater heatwave, combined with an increase in ocean acidity, had destroyed swaths of Australia’s Great Barrier Reef.

This has led marine biologists to warn that all coral reefs risk being destroyed by the end of the century even if carbon dioxide emissions are kept to relatively low levels in future decades. Apart from the impact on one of the world’s greatest natural wonders, the effect on fish stocks, and in particular shellfish, could be grim. Shells of marine creatures are made from calcium carbonate and their formation is disrupted by acidic water.

An example is provided by oyster farms on the Oregon coast. These farms regularly suffer from upwellings of acidic water from deep regions of the Pacific Ocean. When this happens, larval oysters die at the point when they have to form their first shells.

“From the time eggs are fertilized, Pacific oyster larvae precipitate roughly 90 percent of their body weight as calcium carbonate shell within 48 hours,” Oregon State University’s George Waldbusser told the Climate News Network. “They must build their first shell quickly on a limited amount of energy — and, along with the shell, comes the organ to capture external food. It becomes a death race of sorts. Can the oyster build its shell quickly enough to allow its feeding mechanism to develop before it runs out of energy from the egg?”

Increasingly, the answer to this question appears to be no.

This point is summed up by Roberts.

“Prawns, lobsters, clams and scallops — which now dominate our intensively fished seas — all lay down carbonate shells. The fishing industry is therefore badly exposed to risk from more acidic seas. Not only that, acidification threatens the important role that filter-feeding shellfish play in cleansing ocean water. Quite frankly, increased acidity is the last thing marine life needs given all of the other ways in which we are making oceans a tougher place to live,” he said.

Then there is question of just how much seafood is actually eaten today. This turns out to be an issue of considerable controversy, one that was stoked last year in a study — by Daniel Pauly and Dirk Zeller of the University of British Columbia — that was published in the Nature Communications online journal.